1. Field of the Invention
The present invention relates to a projection screen device having a high luminance adapted for use in an overhead projector, a video projector or a liquid crystal projector.
2. Prior Art
A screen film of a projection screen device is subjected to a minute mat processing for forming a superior image on the surface of the screen film. The screen film is classified into a reflection type (i.e. opaque screen) and a transmission type according to an image formation, a flat type and a curve type (concave surface) according to the cross section of the screen, and a nondeformable type and deformable type according to the manner of storage thereof when not used. As the deformable type, there are folding manner and winding manner. A combination of these types form various types.
There has been conventionally, as the image reflection screen, adopted a white cloth or a vinyl cloth having glass powder or alminium powder etc. respectively applied thereon so that the image incident light is reflected bright in all directions. However, the opaque screen also reflects the light other than the image light, hence, there was a problem that both the lights are mixed to reduce the contrast of the image and make the image blur. Accordingly, the projection screen was usually placed at a dark place. The opaque screen has a luminence gain of less than 4, low directional characteristic, and is obtrusive in slight unenveness or wrinkle or warp thereon, and can be reduced in its size by winding thereof when not used or carried.
There is a demand to project on a screen in the light at all circumstances which entails to need a screen film capable of an excellent image having a high contrast.
To meet the demand, the opaque screen film reflects the image light projected by the projector effectively to be equally caught by a number of audience. Furthermore, only the image light projected by the projector is to be reflected toward the audience and the light other than the image light shall be reflected in the direction except the audience.
Hence, the light incident to and reflected by the screen film is required to have strong directional characteristic, namely, reflectance toward the audience. Particularly, in the projector for projecting and expanding an image light of a weak luminous intensity such as VP or LCP, the luminous intensity of the image light on the screen is weak, hence the reflectance toward the audience is needed to be improved.
For this purpose, there has been proposed a screen film having a high luminance which employs a reflection film having high reflectance such as an aluminium foil or a film evaporated by alminium and a lens subjected to cylindrical embossed processing is provided in front of the reflection film so that the luminous gain becomes over 10 and the reflection surface is formed in a concave as a primary curve (laterally arc shaped) or a secondary curve (longitudinally arc shaped) so that the reflective direction is restricted.
However, the reflection-concave type screen film requires a complete smooth flat shape since the reflection film surface is high luminous and there is a likelihood of generating a local excessive light and darkness in the part of the image projected on the screen even if slight uneveness, distortion, wrinkle, or slack appear on the screen film.
Accordingly, there has been conventionally adopted the screen film having the property set forth above which is attached to a rigid plate body made of a metal or synthetic resin, etc. having a flat and undeformable surface, and the screen film attached to the metal and the like is fixed to a fixed frame. Hence, the screen film was the undeformable type.
The conventional deformable type screen film requires a rigid plate body to support thereof and is impossible to be wound or disassembled and inconvenient in carrying, storing, attaching thereof and the like. Particularly, inasmuch as there is recently increased a demand for a large screen in view of development of an image information apparatus, the problem of the deformable type screen device is serious.